In recent years, improvements in power output has been sought in automotive alternators due to increases in vehicle loads, while at the same time automotive vehicle engine compartments are becoming increasingly smaller, leaving little mounting space to spare for them. The need for noise reduction is also high, both inside and outside vehicles, and engine noise is being reduced. However, noise from automotive alternators that operate constantly to generate electric power in order to supply power for the electric loads on vehicles has become a problem. Automotive alternating-current dynamoelectric machines are operated over a comparatively wide range of rotational speeds from low speeds to high speeds and wind noise and electromagnetic noise therefrom are considered to be problems. Electromagnetic noise from automotive alternators, particularly in a region from an idling state to a normal service region in which engine speed is low, has a different frequency from that of engine noise and noise from engine auxiliary machinery, and is considered a problem because it is noticeable to human ears and is heard as an unpleasant noise.
Various techniques for reducing electromagnetic noise have been proposed conventionally in answer to needs of this kind. For example, in dynamoelectric machines having two stator slots per phase per pole, electromagnetic vibrational forces generated by harmonic magnetic flux have been reduced by making an armature winding into a wye-delta hybrid connection and forming the stator slots at a uniform angular pitch (such that a slot opening portion pitch has an electrical angle of 30 degrees) to reduce harmonic magnetic flux inside the dynamoelectric machine (see Patent Literature 1, for example).
Patent Literature 1: Japanese Patent No. 3633494 (Gazette)